Hand-held power tool with jamming-detection sensor

ABSTRACT

A hand-held machine tool has a housing, a tool rotatable about a rotational axis, a motor provided with a gear unit and driving the tool in rotation about the rotational axis, the gear unit having at least one rotating part which is arranged so as not to be axially parallel to the rotational axis of the tool, a bearing supporting the rotating part of the gear unit, and a sensor arranged at the bearing so that the sensor lies in an effective region of bearing forces which are produced by a moment of occurring gyroscopic effect when the housing rotates around the rotational axis of the tool.

BACKGROUND OF THE INVENTION

The present invention relates to a hand-held machine tool.

More particularly, it relates to a hand-held machine tool, in particulara drill hammer, which has a housing and a tool driven in rotation by amotor with a gear unit. A hand-held machine tool having a separatebearing block and electrical force measuring device arranged at thelatter for detecting sudden jamming or blockage of the tool is alreadyknown from EP 199 883 A2. This construction requires a speciallydesigned bearing block which is also supported in the machine housing soas to be rotatable at a swivel axis. Since the bearing forces orreaction forces occurring as a result of the transmission of torque aremeasured, there is also a risk of faulty triggering whenmoment-transmitting shocks or impacts occur in normal operation.

SUMMARY OF THE INVENTION

Accordingly, it is an object of the present invention to provide ahand-held machine tool, which avoids the disadvantages of the prior art.

In keeping with these objects and with others which will become apparenthereinafter, one feature of the present invention resides, brieflystated, in a hand-held machine tool which has a sensor arranged at abearing of a rotating part of the gear unit so that it lies in theeffective region of the bearing forces produced by the moment of theoccurring gyroscopic effect when the housing of the hand-held machinetool rotates around the rotational axis of the tool.

When the hand-held machine tool is designed in accordance with thepresent invention, it has the advantage over the prior art that theblocking of a tool can be detected in a reliable and simple mannerwithout additional expenditure on construction. To do this the inventionmakes use of the effect whereby a forced change in position of arotating body which is suspended at least at one point produces anadditional angular momentum directed at a right angle to the deflection.This gyroscopic effect produces reaction or bearing forces in thebearings of the rotating part which do not occur in normal operation.

It is particularly advantageous to arrange the sensor or sensors on aline extending parallel to the rotational axis of the tool and throughthe center axis of the rotating part, particularly of the motor. Thesensor can be constructed as a force measuring device or as a pressuresensor. It is also particularly advantageous if the rotating part isformed by the armature of the motor. As a result of the large massmoment of inertia of the armature, this leads to a correspondingly largeadditional angular momentum. The additional angular momentum can bedetected particularly well if the bearing forces occurring in normaloperation act in a different direction, especially so as to be offset by90° relative to the gyroscopic forces. This can be achieved in that thegear members cooperating with the rotating part are arranged in such away that the transmission forces do not act in the direction of therotational axis of the tool, but rather at a right angle thereto. Themeasurement signal of the sensor is fed to a control device which causesan interruption in the rotational driving of the tool, particularly byswitching off the motor or by opening a safety coupling.

The novel features which are considered as characteristic for theinvention are set forth in particular in the appended claims. Theinvention itself, however, both as to its construction and its method ofoperation, together with additional objects and advantages thereof, willbe best understood from the following description of specificembodiments when read in connection with the accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 shows a section through a hand-held machine tool formed as adrill hammer.

DESCRIPTION OF PREFERRED EMBODIMENT

A drill hammer 1 with a housing 2 and a tool carrier 3 which projectsout of the housing and in which a drilling tool 4 is inserted is shownschematically in FIG. 1. A hammer mechanism which is accommodated in thehousing 2 is not shown in the drawing. The drilling tool 4 is driven soas to rotate around its axis of rotation 5 by a spindle 6 supporting thetool carrier 3. The spindle 6 is connected in turn with a shaft 11 of anelectric motor 12 via two bevel gears 8, 9 forming a gear unit 7. Of themotor, only the part 14 rotating around its center axis 13, i.e. thearmature, is shown in the drawing. The center axis 13 lies verticallywith respect to the rotational axis 5 of the tool 4. The shaft 11 issupported in two bearings 16, 17 which are rigidly connected with thehousing and can be constructed e.g. as roller bearings. The motor shaft11 and the spindle 6 are so disposed in relation to one another that thebearing forces in the bearings 16, 17 act in a plane situated verticallyrelative to the spindle 6, that is, in a plane parallel to the bevelgear 8. Thus, when the tool 4 is driven in rotation to the right theoperating bearing force F_(L1) occurs in the bearing 16 and theoperating bearing force F_(L2) occurs in the bearing 17.

The drill may jam when the drilling tool 4 penetrates a workpiece 19.This means that the angular velocity ω_(W) of the drilling tool 4suddenly drops to zero. The motor 12 which continues to run now causesthe housing 2 to rotate to the left around the rotational axis 5according to the arrow designated by ω_(G),B. Accordingly, the rotatingpart 14 of the motor 12, which may now be considered as a gyroscope, islikewise deflected from its rest position so as to rotate to the leftaround the axis 5. This produces a change in the torsion vector orangular momentum vector as occurs when a gyroscope is deflected out ofits rest position.

The moment of the gyroscopic effect M_(K) is brought about by the forcedchange in the torsion vector:

    M.sub.K =dD/dt=ω.sub.G,B ×D

    or

    M.sub.K =ω.sub.G,B ×ω.sub.A ×I.sub.A,

where

ω_(G),B =the angular velocity of the housing in the event of jamming

ω_(A) =the angular velocity of the armature

I_(A) =the mass moment of inertia of the armature

The moment of the gyroscopic effect M_(K) generates additional bearingforces F_(K) in the bearings 16 and 17 which act at a 90-degree offsetrelative to the operating bearing forces F_(L). In the effective regionof the bearing forces F_(K), a sensor 20 for measuring these forces isarranged at least at one of the bearings 16, 17. The sensors can beforce measuring devices or force or pressure sensors which can bearranged in particular between the housing 2 and the bearings 16, 17.

The measurement signal of the sensor or sensors 20 is transmitted to acontrol device 21 which receives the level of the measurement signaland/or its shape, as the case may be, and causes the rotational drivingof the tool 4 to be interrupted if a jammed tool is detected. This canbe effected either in that the motor 12 is turned off or by triggering asafety coupling 22, known from the prior art, in the drive train betweenthe motor 12 and the tool carrier 3. This safety coupling 22 promptlyseparates the motor 12 from the tool 4 so as also to prevent the housing2 from rotating too far in the event of jamming.

The measurement signal obtained in the manner described above clearlyshows a case of jamming, since no moment-transmitting shocks occur inthe direction F_(K) transverse to the operating bearing forces F_(L) innormal operation. This prevents inappropriate triggering. The use of thegyroscopic effect has the further advantage that its magnitude dependson the torsional velocity of the housing and accordingly automaticallyadapts itself to the attitude of the operator. When the operator holdsthe housing 2 in such a way that no twisting occurs, the tool is alsonot separated from the motor. The full force of the machine can then beutilized for rotary drilling work.

It will be understood that each of the elements described above, or twoor more together, may also find a useful application in other types ofconstructions differing from the types described above.

While the invention has been illustrated and described as embodied in ahand-held machine tool, it is not intended to be limited to the detailsshown, since various modifications and structural changes may be madewithout departing in any way from the spirit of the present invention.

Without further analysis, the foregoing will so fully reveal the gist ofthe present invention that others can, by applying current knowledge,readily adapt it for various applications without omitting featuresthat, from the standpoint of prior art, fairly constitute essentialcharacteristics of the generic or specific aspects of this invention.

What is claimed as new and desired to be protected by Letters Patent isset forth in the appended claims:
 1. A hand-held machine tool,comprising a housing; a tool rotatable about a rotational axis; a motorprovided with a gear unit and driving said tool in rotation about saidrotational axis, said gear unit having at least one rotating part whichis arranged so as not to be axially parallel to said rotational axis ofsaid tool; a bearing supporting said rotating part of said gear unit;and a sensor arranged at said bearing so that said sensor lies in aneffective region of bearing forces which are produced by a moment ofoccurring gyroscopic effect when said housing rotates around saidrotational axis of said tool.
 2. A hand-held machine tool as defined inclaim 1, wherein said sensor is arranged on a straight line extendingparallel to said rotational axis of said tool and passing through acenter axis of said rotating part.
 3. A hand-held machine tool asdefined in claim 1, wherein said sensor is a force sensor.
 4. Ahand-held machine tool as defined in claim 1, wherein said sensor is apressure sensor.
 5. A hand-held machine tool as defined in claim 1,wherein said rotating part is formed as an armature of said motor.
 6. Ahand-held machine tool as defined in claim 1, wherein said housing, saidtool and said motor with said gear unit are arranged so that the bearingforces produced by the moment of the occurring gyroscopic effect act ina different direction than bearing forces occurring in normal operation.7. A hand-held machine tool as defined in claim 6, wherein said housing,said tool, and said motor with said gear unit are arranged so that thebearing forces produced by the moment of the occurring gyroscopic effectact transversely to the bearing forces occurring in normal operation. 8.A hand-held machine tool as defined in claim 1, wherein said gear unithas gear unit members cooperating with said rotating part and arrangedso that transmission forces occurring in normal operation in said gearunit do not act in a direction of said rotational axis of said tool. 9.A hand-held machine tool as defined in claim 1; and further comprising acontrol device which causes an interruption of the rotation of saidtool, said sensor being arranged so as to transmit a measurement signalto said control device for causing an interruption of the rotation ofsaid tool.
 10. A hand-held machine tool as defined in claim 9, whereinsaid control device is formed so as to cause said motor to be shut off.11. A hand-held machine tool as defined in claim 9; and furthercomprising a safety coupling, said control device being formed so as tocause said safety coupling to be opened.